The present invention relates to a color filter which enables the production of a liquid crystal display excellent in display qualities, and a photosensitive resin composition for forming a pattern which can be used for the production of this color filter.
Recently, a color liquid crystal display apparatus is noticed as a flat display. As one example of the color liquid crystal display apparatus, an apparatus is exemplified in which a color filter constituted of a black matrix, a colored layer of a plurality of colors (usually, three primary colors of red (R), green (G) and blue (B)), an orientation layer and a transparent conductive layer (common electrode), and a TFT array substrate constituted of a thin film transistor (TFT element), a picture element electrode and an orientation layer are allowed to face each other at a predetermined clearance, and a liquid crystal material is injected into this clearance part to give a liquid crystal layer. In such a color liquid crystal display apparatus, the clearance part constitutes the thickness itself of the liquid crystal layer, and for enabling excellent display abilities such as high speed responsiveness, high contrast ratio, wide visibility angle and the like required for color liquid crystal display apparatuses, it is necessary to strictly keep the thickness of the liquid crystal layer, namely, the clearance distance between the color filter and the TFT array substrate at a constant value.
Conventionally, as a method of determining the thickness of a liquid crystal layer in a color liquid crystal display apparatus, there is a method in which particles or rod bodies, called spacer, made of glass, alumina, plastic and the like are dispersed in large amount on a color filter or a TFT array substrate, the color filter and TFT array substrate are pasted and a liquid crystal is injected between them. The size of the clearance part between both substrates, namely, the thickness of a liquid crystal layer is determined by the size of the spacer.
However, in the above-mentioned method of forming a clearance part between a color filter and a TFT array substrate, the following problems occur regarding the motion of a color liquid crystal display apparatus. Namely, a clearance part having uniform size over the whole surface of the color liquid crystal display apparatus is not formed, unless the density of a spacer dispersed on the surface of a substrate is appropriate and spacers are dispersed uniformly on the surface of a substrate. In general, when the dispersion amount (density) of a spacer is increased, the uneven variation in thickness of the clearance part decreases, however, when the dispersion amount (density) is increased, the number of spacers present on display picture element part also increases, and this spacer constitutes a foreign matter in a liquid crystal material at the display picture element part. Owing to the presence of the spacer, disturbance occurs in the orientation of a liquid crystal molecule regulated by an orientation film, liquid crystal only around the spacer shows a problem that orientation control by ON and OFF of voltage becomes impossible, and the like, and a problem is found that display abilities such as contrast ratio and the like decrease.
To solve such problems, a color filter equipped with a columnar convex part for determining clearance (thickness of a liquid crystal layer) is suggested (JP-A No. 4-318816, and the like). In this color filter, a colored layer is formed, a protective layer is formed so as to cover this colored layer, then, a columnar convex part is formed at a predetermined position on a black matrix by a photolithography process using a photosensitive resin.
In general, a photosensitive resin used in conducting pattern formation by pattern exposure and development contains a monomer, polymer and photopolymerization initiator. However, the above-mentioned columnar convex part formed by using such a conventional photosensitive resin has a problem that, under high temperature and high pressure in fabricating (cell press fitting) a color filter and TFT array substrate, plastic deformation amount increases, causing a deterioration in a function as a spacer. Further, if the hardness of the columnar convex part is enhanced for solving this problem, this part cannot follow the shrinkage of liquid crystal in a wide practical temperature range (xe2x88x9220 to 40xc2x0 C.) and foaming occurs in the liquid crystal layer, leading to a problem of reduction in display qualities such as decoloring, uneven color and the like.
The present invention has been achieved in order to solve the above problems. It is an object of this invention to provide a photosensitive resin composition which enables the formation of a pattern manifesting large elastic deformation ratio and small plastic deformation ratio in a wider temperature range, and a color filter which enables the production of a liquid crystal display having a columnar convex part for setting the thickness of a liquid crystal layer and having excellent display qualities.
For attaining such an object, a liquid crystal display color filter of the present invention has a constitution comprising a substrate, a colored layer of a plurality of colors formed on the substrate in a predetermined pattern, and a plurality of columnar convex parts, wherein the columnar convex part manifests an elastic deformation ratio [(elastic deformation amount/total deformation amount)xc3x97100] ranging from 40 to 60% and an initial deformation ratio [(initial deformation amount/original thickness)xc3x97100] ranging from 10 to 30%, at a temperature of 180xc2x0 C.
The photosensitive resin composition of the present invention has a constitution comprising at least a polymer, poly-functional acrylate monomer and a photopolymerization initiator, wherein the content of the poly-functional acrylate monomer is in the range from 50 to 70% by weight.
Further, the photosensitive resin composition of the present invention has a constitution comprising at least a polymer, a monomer having an unsaturated double bond, a photopolymerization initiator and an alicyclic compound-containing resin, wherein the alicyclic compound-containing resin contains as an alicyclic compound a compound having a poly-cyclic steric structure.
In another embodiment of the above-mentioned photosensitive resin composition, the above-mentioned alicyclic compound-containing resin is obtained by polymerizing a monomer prepared by adding a vinyl group and/or an isopropenyl group to the above-mentioned alicyclic compound.
In still another embodiment of the above-mentioned photosensitive resin composition, the above-mentioned monomer is a poly-functional acrylate monomer, and the above-mentioned vinyl group and isopropenyl group have a carboxyl group on one of double bond carbons.
In further another embodiment of the above-mentioned photosensitive resin composition, an epoxy compound is contained in the composition.
In the present invention thus described above, a poly-functional acrylate monomer contained at predetermined high concentration in a photosensitive resin composition, or an alicyclic compound-containing resin contained in a photosensitive resin composition, imparts a large elastic deformation ratio and a small plastic deformation ratio in a wider temperature range to a pattern, and a columnar convex part formed by using this photosensitive resin composition manifests small plastic deformation amount under high temperature and high pressure in cell press fixing and can follow the shrinkage of liquid crystal in a wider temperature range (xe2x88x9220 to 40xc2x0 C.), causing no deterioration in a function as a spacer.
As described above, according to the present invention, the concentration of a poly-functional acrylate monomer contained in a photosensitive resin composition is as high as 50 to 70% by weight or a photosensitive resin composition contains an alicyclic compound-containing resin, therefore, a pattern formed by performing exposure, development and heating treatment manifest large elastic deformation ratio and small plastic deformation ratio in a wider temperature range. In a color filter having a plurality of columnar convex parts formed by using this photosensitive resin composition, the columnar convex part has an elastic deformation rate [(elastic deformation amount/total deformation amount)xc3x97100] of from 40 to 60% and an initial deformation rate [(initial deformation amount/original thickness)xc3x97100] of from 10 to 30% at 180xc2x0 C., the plastic deformation amount under high temperature and high pressure in cell press fitting is small, the convex part can follow the shrinkage of liquid crystal in a wider temperature range (xe2x88x9220 to 40xc2x0 C.) and an function as a spacer can be maintained constantly. Therefore, the color filter of the present invention can be applied also to color liquid crystal displays in which high precision in control of the thickness of a liquid crystal layer is required, for example, to color liquid crystal displays of IPS (In-Plane Switching) liquid crystal mode, and color liquid crystal displays excellent in display quality and having high reliability can be obtained.